The present document is based on Japanese Priority Document JP2002-079163, filed in the Japanese Patent Office on Mar. 20, 2002, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a polishing method and a polishing apparatus, and more particularly, to a polishing method and a polishing apparatus which polish a work surface still having unevenness thereon with slurry containing particles.
2. Description of the Related Art
As disclosed in Japanese Patent Application Laid-Open No.11-288906, a CMP (Chemical Mechanical Polishing) method has widely been used conventionally in the process of planarizing a semiconductor wafer substrate.
Especially, an enhanced integration degree of VLSI circuits causes an increase in number of wiring layers, and improving planarization process with CMP method is strongly required. The planarization process can be possible by realizing selective polishing on protrusions of a surface. Conventionally, a polishing pad is pressed to the surface at constant pressure so as to increase the speed at which the protrusions are selectively polished and removed with the aid of pressure distribution difference between the protrusions and depressions. However, since the method cannot produce a sufficient difference in the pressure distribution, there is a limitation on the ability to reduce unevenness. Thus, a method which actively allows a material process in an arbitrary fine region has been needed.
As shown in FIG. 1, the conventional CMP method involves adhering and fixing an elastic polishing pad 12 onto a rotating polishing plate 11. A silicon wafer 13 is fixed to an end face of a polishing head 14. The silicon wafer 13 is fixed by compression to the polishing pad 12 with its surface to be polished facing downward. Slurry 15 is supplied in this state, and the polishing plate 11 is rotated and the polishing head 14 is also rotated to polish the surface of the silicon wafer 13.
At this time, since the polishing pad 12 is in contact with the silicon wafer 13 with pressure exerted on each other, the slurry 15 is not sufficiently flowed into the polishing region to result in unstable polishing. To prevent this, the surface of the polishing pad 12 is dressed with a diamond tool or the like so as to make relatively large protrusions and depressions for slurry pools. Thus, because the surface of the polishing pad 12 is made of elastic material, it becomes fuzzy due to the protrusions and depressions for the slurry pools and scratching with the dressing tool.
As shown in FIG. 2, the silicon wafer 13 to be polished with the CMP method as shown in FIG. 1 has regular protrusions and depressions such as wiring pattern 21 of conductive metal at a surface layer and a thin film layer 22 serving as an insulating film made of SiO2 formed over the protrusions and depressions. Affected by the protrusions and depressions of the wiring pattern 21, protrusions and depressions are generated at the surface of the thin film layer 22. In the planarizing process with the CMP method, selectively polishing on only the protrusions 23 of the protrusions and depressions of the thin film layer 22 achieves a surface planarization.
Attempts have been made to bring the polishing pad 12 into contact only with the protrusions on the surface of the silicon wafer 13 to perform polishing by increasing the elasticity of the polishing pad 12, by way of example. Actually, however, as shown in FIG. 3, because the polishing pad 12 is formed of an elastic body which is deformed under pressure and its surface is fuzzy, the surface of the polishing pad 12 contacts not only the protrusions 23 of the thin film layer 22 but also the depressions. In other words, it is difficult to perform selectively polishing on only the protrusions 23.
For this reason, it is difficult to achieve an ideal planarization process in which largely remove material including only the protrusions 23 as shown by a removed region 24 in FIG. 4 for selectively removing the protrusions 23. Specifically, in reality, there exists a problem that the removed region 24 has a substantially uniform thickness regardless of the presence of the protrusions and depressions as shown in FIG. 5 to substantially uniformly polish the protrusions and depressions of the thin film layer 22 made of SiO2 formed on the surface of the silicon wafer 13 even with the progression of the polishing, thereby preventing successful planarization.
When planarizing a surface having protrusions and depressions thereon, it is necessary to selectively remove only the protrusions. In typical CMP, however, since the surface of the polishing pad has large protrusions and depressions for holding slurry and is dressed to have fuzz as fibers, the polishing pad is not in contact uniformly with the silicon wafer. When the protrusions are removed with the progression of the polishing, the depressions are also simultaneously removed, although the removing amount is smaller. For this reason, planarization in a short time is difficult in polishing the surface having the protrusions and depressions. Also, even when polishing the surface is performed in a long time, a favorable planarized surface is difficult to achieve although its steps are reduced.
This phenomenon is also seen in processing of an aspheric lens. Specifically, in general, high precision grinding process is performed to form a desired aspheric shape on the surface of a lens, and then a polishing process is performed to remove a surface damage layer and ensure surface roughness as optics device simultaneously.
In the polishing process, even when previously measurements are made to calculate polishing regions and removing amounts at those regions, a shape of the region to be removed through the polishing has a certain area and thus its surroundings are processed at the same time, meaning that regions other than the intended region are subjected to processing. As a result, the polishing process deteriorates the accuracy achieved through the grinding process.
In view of the above-described problems, the present inventors have proposed a method as shown FIG. 6, in Japanese Patent Application Laid-Open No. 2000-289444. The method can be carried out local and selective polishing the protrusions 23 of the thin film layer 22 formed on the silicon wafer 13 by selectively irradiating laser light to the protrusions 23 so as to form aggregation trace of particles of the slurry there, and then performing polishing to break the aggregation trace of particles to result in a high concentration of the slurry in a local region.
According to the above-mentioned method, however, most of the polishing time is spent on polishing the aggregation trace, and an only extremely short time is spent on removing the material of the protrusions 23 immediately before the aggregation trace are eliminated. Thus, the method has disadvantages of an insufficient ability of planarization and low efficiency of planarization.
The present invention has been made in order to solve or alleviate such problems, and there is a need to provide a polishing method and a polishing apparatus which polish a work surface having protrusions and depressions thereon to efficiently achieve a target flat or curved surface by polishing and removing a relatively large material amount of the protrusions.
The present invention relating to the polishing method provides a method of polishing a work surface having protrusions and depressions thereon with slurry containing particles, comprising the steps of:
forming aggregation trace within the depressions by collecting the particles of the slurry through irradiating laser light to the depressions existed adjacent to or in the vicinity of the protrusions where a selectively larger removal material amount is desired during polishing process, whereby regions having the aggregation trace become substantially same height as the protrusions; and
planarizing by polishing the regions having the aggregation trace and the protrusions together so as to remove a substantially uniform material amount.
Preferably, the aggregation trace of the particles are formed within the depressions of the work surface by determining a path on which laser light flux moves in accordance with the shape of the protrusions and depressions of the work surface to perform scanning. Alternatively, the aggregation trace of the particles are preferably formed within the depressions of the work surface by laser light irradiation through a light shield mask, the light shield mask is arranged in accordance with the shape of the protrusions and depressions of the work surface and placing in a path of laser light. In addition, preferably, the aggregation trace of the particles are formed in a region irradiated with laser light of the work surface by trapping and collecting the particles of the slurry through a laser trapping phenomenon with light radiation pressure, the formed aggregation trace of the particles are broken by polishing and the particles are used as polishing particles, so that the particles are concentrated near the region irradiated with laser light, and then an amount of removal material by polishing near the aggregation trace of the particles is increased. It is also preferable that the shape of a surface of a region to be polished on the work surface is measured and stored before or during polishing. A laser light irradiation position, an irradiation condition, and a polishing condition are calculated from the measurement data, and laser light irradiation is performed in accordance with the calculation results.
One aspect of the present invention relating to the polishing apparatus provides a polishing apparatus for polishing a work surface having protrusions and depressions thereon with slurry containing particles, including:
a laser optical system for projecting and irradiating laser light; and
a polishing tool system for performing press in an axis direction and rotational movement,
wherein irradiation of laser light and polishing are performed on the depressions adjacent to the protrusions of the work surface simultaneously and sequentially by relative movement of the laser optical system and the polishing tool system to the work surface.
It is preferable that the shape of a surface of a region to be polished on the work surface is measured by shape measuring means before or during polishing, the measured shape is stored by storing means. A laser light irradiation position, an irradiation condition, and a polishing condition are calculated from the stored measurement data. Based on the calculation result, the laser optical system irradiates laser to the depressions adjacent to the protrusions or the polishing tool system polishes the protrusions and the depressions. In addition, a light shield mask is placed in an optical path of the laser optical system in order to irradiate laser light selectively in accordance with the shape of the protrusions and the depressions of the work surface.
When forming the aggregation trace by the laser trapping phenomenon and improving the flatness of the work surface such as a silicon wafer using the aggregation trace, in order to remove only the material of the protrusions during the polishing process, a mask may be provided on the material of the depressions for protection. FIG. 8 shows the concept of a planarization process based on such an idea, that is, an LAFP (Laser Aggregation, Filling-up and Polishing) method.
After laser light flux is irradiated to the depressions of the protrusions and depressions of the surface of the silicon wafer and form the aggregation trace selectively to fill up the depressions, polishing is performed on the region where the aggregation trace are formed. When the aggregation traces are not formed, polishing causes removal of the depressions, and the steps of the protrusions and depressions are not eliminated. However, when the aggregation traces are formed to fill up the depressions by the LAFP method, polishing is performed maintaining flatness. The final polishing surface no longer has the original shape of the surface having the protrusions and depressions, and a planarized surface is formed.
When the specific region of the workpiece is polished with the small tool by the above-mentioned LAFP method, the polishing can be performed with high precision regional resolutions. In CMP planarization process for the surface having the fine protrusions and depressions thereon in the semiconductor process, selectively polishing on the protrusions can be possible. As a result, high flatness can be obtained. Also, planarization of the interlayer insulating film mainly made of a SiO2 based material can be possible. In addition, planarization of an insulating layer over a metal film made of Cu or the like can be possible. Such a technique is capable of being applied to high precision polishing of an aspheric lens or the like, so that polishing the aspheric lens with high precision can be possible.
Therefore, according to the polishing method of the present invention, in planarization process of the work surface having the protrusions and depressions, especially removing the protrusions selectively by polishing, is possible and high flatness can be achieved.
According to the polishing apparatus of the present invention, it is possible to perform selectively irradiation with the laser light and polishing simultaneously or sequentially the depressions adjacent to the protrusions on the work surface. Therefore, the polishing apparatus capable polishing achieving high flatness by selectively polishing the specific region on the work surface can be provided.